The issue is that False is causing a read from stdin, since False == 0.

>>> open(0).readlines()
test
['test\n']

Here I typed "test", followed by Ctrl-D (end of file). readlines() then completed and printed its result.

I think the basic answer here is "don't do this". It's not a bug, and is documented.

https://docs.python.org/3/library/functions.html#open
says:
file is a path-like object giving the pathname (absolute or relative to the current working directory) of the file to be opened or an integer file descriptor of the file to be wrapped.

So an integer file descriptor False is causing stdin to be wrapped.

>>> False == 0
True
>>> isinstance(False, int)
True